Oxytocin the Key to Monogamy, Study Finds

The secret to making true love last? Oxytocin, according to a study published in the Proceedings of the National Academy of Sciences.

Called the love hormone, oxytocin is perhaps bettered termed the "bonding hormone," say researchers from the Universities of Bonn and Chengdu, as well as the Ruhr University of Bochum.

The scientists used functional magnetic resonance tomography (fMRI) to examine the brains of 40 heterosexual men in permanent relationships as they were shown images of their female partner, as well as other women. The men were first given a dose of oxytocin, and then later a placebo.

"When the men received oxytocin instead of the placebo, their reward system in the brain when viewing the partner was very active, and they perceived them as more attractive than the other women," lead author Dirk Scheele said in a statement.

The researchers then tested whether oxytocin increased the activation of the reward system only when the partner was presented, or if a similar effect would occur when the men were shown images of acquaintances or female work colleagues they had worked with for many years.

As it turned out, the effect could only be created when the men were presented with a picture of their significant other.

"This biological mechanism in a couple relationship is very similar to a drug," explained Dr. Rene Hurlemann, executive senior physician at the Inpatient and Outpatient Department of Psychiatry and Psychotherapy of the Bonn University Medical Center.

According to Hurlemann, this effect may help explain why individuals experience such profound melancholy after they are separated from or lose a partner. "Due to the lack of oxytocin secretion, the reward system is understimulated, and is more or less in a withdrawal state."

This bond is also important in providing evidence as to why monogomy evolved, despite the fact that men with many partners have the advantage in disseminating their genes.

"When oxytocin strengthens the partner bond, it increases the stability of the persons providing nutrition and thus the chances of survival for the progeny," Hurlemann said.